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by ReptiloidTakingOverTheWorld



Category: Kingdom Hearts, 僕のヒーローアカデミア | Boku no Hero Academia | My Hero Academia
Genre: Angst, Fluff, Gen, Not Canon Compliant, Not Serious, Other Additional Tags to Be Added, Parental Yagi Toshinori | All Might, Post-Kingdom Hearts Birth By Sleep, Redemption, Seriously not at all, Vanitas Is Bad at Feelings (Kingdom Hearts), Vanitas is 4, Yagi Toshinori | All Might is a Dork
Language: English
Status: In-Progress
Published: 2019-11-10
Updated: 2019-11-11
Packaged: 2021-01-26 16:31:00
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 2
Words: 2,891
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/21377131
Author URL: https://archiveofourown.org/users/ReptiloidTakingOverTheWorld/pseuds/ReptiloidTakingOverTheWorld
Summary: After his fight with Ventus, Vanitas wakes up in the Keyblade Graveyard. If that wouldn’t be confusing enough, he ended up in a version of his body, that’s four years old.Trying to find a way to get rid of the Unversed for good, he ends up in a new world, filled with heroes and villains. And of course, he'll be on the side of villains. ...Right?
Comments: 9
Kudos: 30





	1. Prologue

**Author's Note:**

> Hello!  
This isn't my first time writing, but it is the first time I write in English. (And posting on this site.)  
Basically, this is just my me being a fangirl of two things and mashing them together. If you like Vanitas, this is for you. If you like All Dad, same.  
This fic is only based off the MHA-Anime, I have not read the manga. This is mainly important when it comes to certain characters backstories, which I know are already in the manga, but not in the anime yet. I'll gloss over them for the most part, but still write something that might not be canon compliant. (Just like this whole mess of a fic, tbh)  
Basically this was inspired by a RP with a friend of mine. So uh... yeah. Don't take it too seriously, this is mainly fanservice.

Grumbling, he rolled onto his side. His head hurt, his chest too, just like his limbs. Basically, his entire body hurt. He was used to that. Which is why he didn’t notice anything weird at first.  
Vanitas opened his eyes, just to find himself on the familiar ground of the Keyblade Graveyard. Annoyed at the dazzling sun he decided, that he had to move into the shadows. Why was he even out in the open like this to begin with?  
He was about to stand up, when the memories came crushing down on him. The fight with Aqua and Ventus, getting his hands on the X-Blade and losing it immediately after. A familiar cold settled in, his knees growing weak and he fell to the ground again.  
It didn’t matter. Nothing mattered anymore. He was stuck with the Unversed again. After spending the entirety of his existence working towards this one goal – he achieved it. He barely had it in his grasp, just for it to be pried away mere minutes later.   
Reluctantly he shook his head. Ventus. He needed to find him, now. If Vanitas was okay, his other half might also-…  
He couldn’t feel him. He couldn’t sense where he was. That blonde kid whose happy memories had been pushed onto him for years was gone. Just vanished.  
Incredulous he shook his head, a hand slowly coming up to his chest, just above his heart. Maybe… If Ventus was gone… Was he now inside of him? And since he was stronger than Ventus, Vanitas had the control, instead of him?  
There was an easy way to find out. A very easy one. But he hesitated. He was scared. Something he’d never admit out loud, but it was true. Because if he was able to create Unversed now, he would always be. Without Ventus it was impossible to get rid of them. This was the moment of truth.  
He spent minutes simply staring at a rock in front of him. He knew, he had to do it, but something told him, he wouldn’t like the answer. It was a quiet voice in the back of his head, growing louder and louder until it took over everything in his mind.  
Gritting his teeth and clenching his fists, he clenched his eyes shut, deciding to just get over it. Vanitas used the fear he felt, just like he did countless times before, to form an Unversed, a Flood specifically.  
_It’s not there _ , he prayed, _ There’s nothing there._  
Breathing heavily he opened his eyes. He was not alone. Before him was Flood, moving it’s triangular head from side to side, like it’s kind always did.  
Vanitas slumped down in defeat. There was nothing he could do. These monsters, the pain they bring him and others would always be with him. There was no way around it.  
And even worse, everything he endured to this point on was pointless. Everything he did, all the training – it didn’t matter.  
He felt like crying. But instead, he just laughed. Staring up at the sky he laughed. Of course things would turn out like this. From the very first moment of his existence, he knew, that he’d always get the short end of the stick.  
His other half found a loving family, a master who’d pamper him and got his side effects of their separation fixed without even moving a single finger.  
Vanitas on the other hand ended up with Xehanort, who checked in on him twice a week if he was unfortunate enough and emotions that would kill him, if he didn’t watch out for them. And furthermore he was the one stuck with their memories from before they got ripped apart. He still remembered their parents, how loving they were, how they were killed by Heartless and how they’d hate him, if they were still alive. After all, he was pure darkness, so how _ could _ they possibly accept him?  
No, they’d accept Ventus, who forgot them and never cared about remembering. It just was not fair. He could feel how the Unversed were forming around him. But there was nothing he could do about it. There was no way, he could suppress his emotions right now.  
And it didn’t matter. He was always able to feel Ventus, feel his very existence, occasionally _ even his emotions _ but now there was nothing. Apparently Xehanort had also given up on him – otherwise that bastard would have already shown up to monologue about his next plan. Either that, or he was dead. Vanitas sincerely hoped it was the latter.  
…Or maybe not.  
Slowly he stood up again. If Xehanort was still alive, he’d personally change that. If he was screwed over by him, he could at least have his revenge. After all, without the X-Blade there was no reason for him to cooperate.  
He looked around at the Unversed surrounding him. Floods, Scrappers, Bruisers… Different types. They had not attacked him yet. For now they were under his control, but that would change soon. He was too shaken up to control them for long. He had to eliminate them quick. It would hurt, but it would be worse, if he actually had to fight them.  
It was when he summoned Void Gear, that he noticed, something was off. His Keyblade was heavier than usual and looking at it, he realized, it was also bigger.  
…No. It wasn’t just Void Gear. The Unversed were also taller.  
Irritated he lowered his weapon. What in the world…?  
He looked down. The ground was also much closer than usual. Had his legs always been this short?  
It took Vanitas a few seconds to understand it. It wasn’t Void Gear nor the Unversed, who’s size changed. _ It was him _. He shrunk.  
Shaking his head he got a hold of his weapon again. He could worry about that once the Unversed were taken care of. After all this wasn’t the first time he had to use more strength then usual to lift his sword.  
However he soon realized, that this was not the only difference. His speed was not up to par, just like his swings were weaker.  
And killing the first flood, he notice something else. The pain was much stronger than usual. His knees gave in and he had to use his sword as a crutch to not fall. What the hell was going on?  
Did… Ventus’ disappearance change his relationship with the Unversed?  
Great! So his efforts weren’t just meaningless, they also made his situation worse.  
He sighed and decided, that he’d kill them with magic for now. That was easier than lifting his sword while his chest felt like it was getting crushed by a meteor.  
Of course, his magic was also weaker. And after eliminating the three Bruisers, he was out of Mana. And to make matters worse, he could feel how he slowly lost the control over the remaining Unversed. The most dangerous ones were gone, but there was still a dozen left of the smaller ones. Which wouldn’t have been a problem, if his body didn’t shrink around ten sizes.  
He could use this chance to open a Corridor of Darkness but he refused to run away. So what if he was smaller? Those Unversed were some of the weakest kinds. If he backed down now, he’d be dead in a few days. It was only a matter of time until a stronger Unversed showed up.  
So he just did the same thing as always. Gritting his teeth, clenching his fists and pushing through, ignoring how tired he felt.  
He had seen worse, he told himself. After all, he could go a day or two without sleep. Nothing Vanitas hadn’t done before. …But something he’d never done in this weak body before.  
Two Floods. That were all the Unversed he could destroy, before he lost the control over the creatures. Great. Now he had to actively dodge them.  
It was just then, when he noticed quick movements out of the corner of his eyes. Prepared to duck himself beneath the arm of a Flood – because apparently he was small enough to do that now – he turned around, just to see a flash of black and red.  
The next thing he knew was the exploding pain in his chest. Distantly he realized, that the remaining Unversed had just been destroyed all at once. His knees gave in and he was on the ground once again. Cursing mentally he tried his best to steady his breathing and get back on his feet. The Unversed might be gone but whoever killed them was still around.  
“So he did tell the truth.”  
The voice was deep, menacingly. And most importantly familiar. His heart skipped a beat and a shiver ran down his spine. It couldn’t be him, right…?  
His sight was blurred, yet he still tried to lift his head and focus on the person before him. The effort was meaningless. His world turned black and he fell into unconsciousness. 


	2. Chapter I: New Alliance

Vanitas wasn’t used to waking up in a bed. Which is why he immediately knew, something was off, when he woke up on the soft mattress beneath a warm and fluffy blanket.   
He sat up, looking around in the small room. The light coming through the window told him, that it was somewhen in the afternoon – in whatever world he was. There wasn’t much furniture in the room, just the bed he was in and a cupboard next to it. Otherwise there was nothing besides the dark blue carpet on the floor.  
The fact that he was inside a house told him, that it wasn’t Xehanort who brought him here. He’d have just let him lie on the ground.  
“Guess this counts as an upgrade…”, he mumbled before getting out of the bed. Which reminded him, that he was indeed still small.  
There were two things he needed to find: The person who brought him here and a mirror. Preferably not in that order.  
So the only door the room seemed like the best option. Opening it, Vanitas found a hallway to his left, another door in front of him and a wall to his right. Before entering any other rooms, he decided to check out the rest of the hallway. It was straight and ended in another door. It was a little bit wider at that end, giving room for a small wardrobe, which was empty, besides a coat, that probably belonged to rather tall man.  
It was most likely an apartment complex and the door would lead to the outside. However based on how empty everything seemed, it didn’t look like someone was actually living here. Or at least not for long.  
He shook his head and turned to the room in front of him. He opened the door and found a small bathroom. Just like the other room, it only had the most important pieces of furniture, in this case a bathtub, empty shelves and a sink, with a cupboard beneath and a mirror above it. Perfect. Just what he needed.  
…But not everything Vanitas needed.  
Clueless he stood in front of the sink. He was neither tall enough to reach it, nor could he actually look in the mirror. Out of mild desperation and stubbornness he jumped up, gripping the ceramic edge and pulled himself up. At least he seemed to still have _ some _ of his strength, he thought, while he climbed into the sink.  
Looking into the mirror, a small boy, around four years old, looked back. Dumbfounded Vanitas stared at him for at least an entire minute.  
Then, it clicked. That boy was _ him _ . He hadn’t just shrunk, he was entirely rejuvenated. But why? And how? _ And why?! _ __  
Absent minded he raised his hand and touched his cheeks. That was him now, it appeared.  
Well, technically speaking, he was four years old. So his appearance matched that now. But mentally he _ wasn’t _ . He did remember living as Ventus for ten years.  
Annoyed Vanitas looked away and puffed out his cheeks, while crossing his arms in front of his chest. What was he going to do now?  
He looked down. Stop sitting in the sink might be a start. As elegant es ever he climbed out of it and landed on the ground. I didn’t remember being a child being this challenging.  
Now that he somewhat found out what had happened to him, he’d have to find the person who brought him here. It was likely, that he was somewhere in the apartment, since he left his coat. Furthermore there would have been no point in bringing him here in the first place. That man wanted something from him and since he found him in the Graveyard, he’d find him everywhere. He was pretty sure about that.  
He left the bathroom and looked at the remaining two doors. One was a kitchen and one another room, he assumed. The man Vanitas was looking for would probably reside in the latter.  
Opening one of the doors, he could lay his eyes upon the new room. Not, that there was much to look at. Two chairs and a table. But that was not the interesting part.  
One of the seats was taken by a man. He seemed to be around 30 years old, was wearing a black suit and had curly, black hair. In front of him lay some papers, which he was apparently reading.  
Vanitas didn’t have to say anything for him to notice him. “I see, you’re finally awake”, he spoke.  
Another shiver ran down the boy’s spine. He sounded way too much like Xehanort. This couldn’t be a mere coincidence.  
“Why don’t you take a seat?” He gestured to the free chair.  
Vanitas eyed him skeptically, not trusting his intentions. However there was no reason not to listen to him. At least for now. Reluctantly he walked over to the chair and climbed up on it, so he could sit down. “Who are you?”  
“You may call me Sensei for now.” A smile crept upon the mans face. “Xehanort told me about you a while ago.”  
The boy stared at him. He really didn’t know what to make of this. “He… did what?” Xehanort had no intention of making sure that Vanitas was alright, if his plan failed. At least not for his sake. That was something he knew. So why would he tell some guy to pick him up?  
“Well, we did exchange a few favors. Not that this is something you would need to concern yourself with.”  
Vanitas suppressed an annoyed sigh. Of course. It was always something like that. “Sure.” He paused. “I don’t know what he told you, but I can’t sense Ventus.” It hurt to say that. “So no X-Blade, if that’s what you’re after.”  
Sensei shook his head. “I have no interest in that weapon.”  
“Oh?” Vanitas raised an eyebrow. “Then what do you want?”  
“I have an offer for you.” He folded his hands on the table and leaned back. “I heard about that unique skill of yours. The creatures you can create.”  
“The Unversed”, Vanitas threw in. Great. Apparently Xehanort ran around gossiping. Did Sensei also know about the weakness the Unversed brought with them? How many people did Xehanort tell about this?!  
“Exactly. I also know, that you want to get rid of them.”  
Vanitas bit his tongue. That was not possible anymore. The only way out died with that annoying weakling.  
The man watched him closely, not wanting to miss a single bit of the boys reaction. “Which is fortunate for you, since I am capable of taking other people’s abilities.”  
With a blank expression Vanitas stared at the man. Was he dreaming? Was he serious? This couldn’t be real, right? This was way too good to be true. Maybe he was lucky for once. No. He wasn’t. This was one of Xehanorts accomplices. There was no way he would help him without getting something in return.  
He took a deep breath, before he spoke. “Okay. What do you want?”  
“You caught on very quickly. A beneficial trait.” Again, the man smiled. “I will free you of the Unversed. However, before that, I want you to work for me.”  
Clenching his fist, Vanitas listened. He was not surprised. Sensei knew his weak spot and used that to his advantage. Nothing the boy wouldn’t have done himself. “I see. However, currently I have a kid’s body. What can I do in a body like that?”  
“I must admit, I also did not expect that. You have a disadvantage when it comes to physical battle. That may be true.” He paused and looked Vanitas directly in the eyes. “However, the appearance of a child does have it’s benefits. People will let their guard down around you. You will see, certain tasks will even get easier thanks to this.”  
Vanitas kept himself from huffing. “So you want me to trick people and then backstab them?”  
“If you want to phrase it like that.”  
It wasn’t that Vanitas hadn’t tried to kill people before. But this was different. He usually fought openly on the battlefield, with his opponent knowing exactly what they were getting into. He’d prefer that over relying on tricks like this.  
But he didn’t have a choice.  
So instead of refusing, he just asked: “For how long?”


End file.
